This invention relates to containers, and more particularly to plastic containers capable of flexing in response to changes in internal pressure.
Plastic containers for perishable products are often filled at an elevated temperature in a process generally known as hot-filling, which includes filling the product at about 185 degrees F. and immediately sealing the container. After sealing, the contents of the container contract upon cooling, which creates a vacuum condition inside the container.
Many conventional cylindrical containers would deform or collapse under the internal vacuum conditions without some structure to prevent it. To prevent collapse, some containers have panels, referred to as “vacuum panels,” located in the panel sidewall. The vacuum panels are configured to inwardly and easily flex in response to internal vacuum such that the remainder of the container body remains cylindrical. The structure between the vacuum panels, such as vertical posts, is stiff relative to the vacuum panels. Often, the vacuum panels are located about the circumference of the body of the container and then covered by a label that wraps around the circumference to hide the vacuum panels and posts.
Other hot-fill containers have a pair of opposing vacuum panels that incorporate handgrips, which usually are not covered with a label panel to enable gripping. Rather, other portions of the container, such as the cylindrical segments between the handgrips, provide a label surface.
The vacuum panels of many bottles are generally rectangular. Often, deformation of a generally rectangular vacuum panel causes high stress areas at the corners and in the areas outside the vacuum panels near the corner.
There is a need for improved containers that are lightweight and capable of withstanding hot-filling conditions.